This invention relates to door locking mechanisms and, in particular, to an electric door strike having a dual locking mechanism which includes internally mounted solenoids for use in the fail-safe or fail-secure modes of operation.
An electric door strike typically includes a strike case fixedly mounted in a door jamb. The strike case contains a pivotally mounted keeper for retaining the deadbolt and door latch in the strike case under the control of the door-mounted lock mechanism. In addition to the control provided by the local lock mechanism, the keeper can be used to permit opening or securing of the door in accordance with an electrical actuating signal applied from a remote location.
In the fail-secure mode of operation, the premises are secured in the event of a power failure by a locking mechanism that causes the keeper to remain engaged in the strike case in the case of power failure. For the fail-safe operating mode, a power failure results in a release of the keeper thereby allowing a door to be opened without regard to the state (locked or unlocked) of the individual lock thereon.
An electrically operated door strike which can provide fail-secure mode of operation is disclosed in U.S. Pat. No. 3,640,560 to Zawadzki et al. In this door strike, the release of the strike keeper is externally controlled by means of a small solenoid located within the strike case. The solenoid interacts with a locking cam to release the keeper upon receipt of the signal. The locking mechanism is contained within the keeper assembly and does not engage the strike case. As a result, there is no direct contact between the doorjamb and the rotatable keeper and the mechanism is not sufficiently durable determined strong forces by one seeking unauthorized entry.
The provision of both fail-safe and fail-secure modes of operation in a single locking mechanism is accomplished in the electric strike mechanism disclosed in U.S. Pat. No. 5,484,180 to Helmar. The single solenoid mechanism shown therein utilizes a locking yoke which mechanically controls the rotation of the keeper. The mechanical linkage and single solenoid is contained within the housing. The enhanced versatility of the Helmar ""180 mechanism is provided by the use of a reversible plunger enabling the device to function in both modes.
Accordingly, the present invention is directed to an electric door strike having dual solenoids to provide engagement between the plungers and the strike case affixed to the door jamb in the fail secure mode of operation. The use of dual solenoids secures the opposing sides of the keeper to reduce the likelihood of a forced entry. In addition, the subject door strike is readily converted to the fail-safe mode of operation without removal of the strike case from its mounting in the doorjamb. Further, the invention employs plungers having a novel latch head that inhibits tampering when the plungers are extended and the keeper is secured.
The present invention is directed to an electric door strike which includes a strike case for affixation to a doorjamb. The strike case is adapted to receive a bolt from a door lock and a keeper is mounted therein. The keeper is rotatably mounted in the strike case for movement between an open position which allows a lock bolt to exit the strike case and a closed position which secures the lock bolt in the strike case and prevents opening of the door.
The keeper is provided with first and second solenoids, each solenoid having an electrical connection for the application of actuating signals thereto. Each solenoid has a plunger with a latch head thereon for engagement with a receiving socket in the strike case. Access is provided to one of the plungers to allow substitution of a plunger having a different latch head thereon for use in the fail-safe operating mode wherein the door can be opened in the absence of an actuating signal.
In the fail-secure mode, the application of an actuating signal causes the plungers to retract thereby removing the latch heads from the corresponding receiving sockets in the strike case. The dual plungers are extended in the absence of the actuating signals by the action of a biasing link between the plungers which urges the plungers outwardly for engagement with the receiving sockets thereby establishing the fail-secure mode of operation.
The replacement of a plunger used for fail-secure operation with a plunger having a different latch head coupled with a modification of the biasing link provides the fail-safe operating mode for the door strike. The remaining plunger with initial latch head is urged by the biasing link out of engagement with the receiving socket in the absence of an actuating signal. Thus, the present door strike can be utilized as a fail-safe or fail-secure locking mechanism with only minor modification.
The fail-secure mode of operation results in two latch heads being received in corresponding sockets in the top and bottom of the strike case. Thus, the security of locking in the absence of power is greatly enhanced. In the fail-safe mode, a single latch head is used to engage the strike case. This latch head is withdrawn upon a power failure to permit the keeper to be rotated to the open position by applying pressure to the door regardless of the state of the door mounted lock.
To inhibit a dislodging of the latch head from the adjacent receiving socket by the application of an external force, the outer end of the latch head is provided with a non-orthogonal end surface having an undercut. A mating undercut is provided in the receiving socket. As a result, forces tending to move the latch head laterally result in the undercut portion of the latch head engaging the receiving socket. The novel configuration of the latch head and receiving socket limit lateral movement of the keeper when the plunger is extended to enhance the security of the locking mechanism.